Number Of Unmyelinated Fibers Research Articles

Chorda tympani nerve fibers in man.

Four normal human chorda tympani nerves were studied for quantitative data of nerve fibers. The average total number of nerve fibers was 5360 (range, 4941-6020). The average number of unmyelinated fibers was 1835 (range, 1518-2083), or 34% of the total. The diameters of myelinated fibers ranged from 1 to 7 microns, peaking at 2 microns. Most of the unmyelinated axons had a diameter between 0.5 and 2 microns. The importance of the quantitative evaluation of the chorda tympani nerve fibers is stressed in reporting structural changes.

The ultrastructure of intramuscular nerves in amyotrophic lateral sclerosis.

Muscle biopsies of 11 patients suffering from amyotrophic lateral sclerosis (ALS) were examined and the i.m. nerves found in seven of them were examined by electron microscopy. In atrophied muscles there was a marked decrease of myelinated fibers. The ultrastructure of the remaining myelinated axons showed changes in the neurofilaments, mitochondria, and vesicles. There was a decrease in the number of unmyelinated fibers as well as the myelinated fibers. Occasionally, there was an increase of unmyelinated fibers containing small fine axons. There were corpora amylacea in unmyelinated axons and banded structures in the extracellular area of the Schwann cells of the unmyelinated fibers. Some of these findings were considered as the ultrastructural features of degeneration and regeneration in i.m. nerves of motoneurons in ALS.

Peripheral innervation of the stapedius muscle of the cat: An electron microscopic study

The nerve supply to the stapedius muscle of the cat was evaluated with regard to the number and diameters of the myelinated fibers and the number of unmyelinated fibers. An average of 1054 myelinated fibers and 7272 unmyelinated fibers were found. The diameters of the myelinated fibers were from less than 1 μm to 10 μm with the peak between 3 and 4 μm. Studies of Wallerian degeneration after intracranial transection of the VII and VIII cranial nerves indicated that 84% of the myelinated fibers were motor and 16% were sensory. There was no significant change in the number of unmyelinated fibers after transection.

Are there specialezed cold receptors in the skin?

The relative number of unmyelinated fibers of a cutaneous nerve conducting impulses of excitation from mechanoreceptors during contraction of pilomotors without cooling and during cooling of the skin by 10°C at the rate of 1 deg/sec was determined by an integrative colliding impulses method. During deformation of the skin by pilomotors the same mechanoreceptors are excited as are excited during cooling of the skin.

Quantitative analyses of the fiber population in rat chorda tympani nerves and fungiform papillae.

AbstractThe numbers of nerve fibers in 44 intact chorda tympani nerves (CT) from 34 rats were counted on electron micrographic montages of cross‐sections of the nerves. The mean number of fibers was 1,096, consisting of 641 myelinated and 455 unmyelinated fibers. There was no significant difference in the mean number of fibers between CT's from right and left sides, nor was there any significant difference in counts between CT segments taken from the middle ear and those taken from just proximal to the region where the CT joins the lingual nerve. The relative contribution of efferent and afferent fibers in the CT was assessed in 13 animals as follows. Intracranial surgery was performed to cut the root of the facial nerve just proximal to its entrance into the internal auditory meatus on the right side. After 19 to 21 days, to allow Wallerian degeneration of the efferent fibers, counts were made as above. The mean number of afferent fibers in the rat CT was 484 myelinated and 122 unmyelinated (606 total); the intact left CT's from the same animals contained a mean of 616 myelinated and 402 unmyelinated (1,018 total) fibers. The afferent limb of the CT, therefore, contains 79% of the total number of myelinated fibers and only 30% of the total number of unmyelinated fibers. Removal of the superior cervical sympathetic ganglion did not significantly affect the numbers of fibers. In order to determine whether the efferent limb of the CT contributes fibers to the fungiform papillae on the tongue, we compared the number of (CT) fibers in fungiform papillae from “de‐efferented” rat tongues with that from papillae of controls. In order to make this comparison, it was necessary to section the lingual nerve, which contributes about 75% of the total number of fibers to the fungiform papillae. This was done in both the control and de‐efferented animals. There was no significant difference in mean number of fibers in fungiform papillae innervated by a de‐efferented CT when compared with those innervated by an intact CT. There is, then, no evidence from these studies to suggest the presence of an efferent CT component within the fungiform papilla.

Unmyelinated fibers in the trigeminal motor root. Possible relationship to the results of trigeminal rhizotomy.

Spinal ventral roots have been shown by electron microscopy to contain a substantial number of unmyelinated fibers. Physiological studies have confirmed that many of these subserve a sensory function. In this investigation the fiber spectrum of the human trigeminal motor root was studied by electron microscopy and it was determined that up to 20% of fibers were unmyelinated. This accounted for approximately 300 to 1000 fibers per root. Since visceral efferent fibers are thought not to occur in the trigeminal root, it appears likely that these unmyelinated fibers may be afferent in nature. It is believed that the presence of a substantial number of unmyelinated fibers in the trigeminal motor root may account for residual sensation or failure of pain relief after rhizotomy of the trigeminal portio major root.

Chlordecone intoxication in man. II. Ultrastructure of peripheral nerves and skeletal muscle.

Tremors, mental changes, opsoclonus, muscle weakness, gait ataxia, incoordination, and slurred speech developed in several employees in a Virginia chemical plant during the summer of 1974. Epidemiologic and clinical studies suggested that the chlorinated insecticide chlordecone (Kepone) was responsible. Severity of symptoms seemed directly related to dose and duration of exposure. Five sural nerve and six muscle biopsy specimens were examined by light microscopy and electronmicroscopy. The sural nerves were also evaluated by computerized morphometry, which showed considerable decrease in the number of unmyelinated fibers and lesser abnormalities of myelinated fibers. Compared with the nerves of the control subjects, those of patients may have had an increase in Reich and Elzholz bodies, and a modest increase in endoneurial collagen. There were occasional "collagen pockets," stacks of Schwann cell cytoplasmic membranes, redundant Schwann cell cytoplasmic folds, and fewer unmyelinated axons. The skeletal muscles contained increased amounts of lipofuscin and lipidlike droplets in subsarcolemmal areas and within intermyofibrillary spaces; the significance of this is unknown. Fiber size variability, type I predominance, and type grouping were present in three cases. All results strongly suggest that chlordecone is a neurotoxic agent predominantly affecting Schwann cells and unmyelinated fibers of peripheral nerves.

Electron-microscopic analysis of the mouse facial nerve near the geniculate ganglion.

An electron-microscopic analysis of the mouse facial nerve near the geniculate ganglion shows that there are, on the everage, 603 more nerve fibers in the portion of the nerve distal to the geniculate ganglion than there are in the part proximal to the ganglion. The average distal increase in the number of unmyelinated fibers is 444 and that in the myelinated fibers is 165. The somatic motor nerve fibers and the parasympathetic fibers in the mouse facial nerve may not contribute to the distal excess. It is possible that the increase in the number of unmyelinated fibers distal to the geniculate ganglion is mainly due to the presence of postganglionic sympathetic fibers in the facial trunk distal to the geniculate ganglion and the greater petrosal nerve. The distal increase in the number of myelinated fibers may be mainly contributed by the sensory fibers.

Development of dorsal root III afferent fibres in postmetamorphic juveniles of the frog Discoglossus pictus

Fibres of dorsal root III were counted in the frog Discoglossus pictus up to 12 weeks following metamorphosis in both skin-grafted and control frogs. There was a progressive, slight increase in the numbers of myelinated fibres in all animals throughout the investigation. The numbers of unmyelinated fibres, however, increased nearly two-fold between 7 and 14 days postmetamorphosis, there being no differences between skin-grafted and normal frogs. After the maximum values had been reached, the numbers of unmyelinated fibres slightly decreased and remained stable thereafter. Good correlation was observed between the increase in the number of myelinated fibres and the increase in body weight, but not for unmyelinated fibres which were highly variable over all weights examined.

Peroneal muscular atrophy (PMA) and related disorders. II. Histological findings in sural nerves.

Biopsy of the sural nerves distinguished two groups of patients with peroneal muscular atrophy (Charcot-Marie-Tooth): a hypertrophic type and a neuronal type. In patients with the hypertrophic type (10 nerves), 30-100 per cent of teased fibres of the sural nerve had demyelinated segments, numerous onion-bulb formations and often an increase in endoneurial space. Large and small fibres, with a diameter of more than 7 micron and less than 5 micron were diminished in number. Regeneration was scarce. There were more fibres with 60-120 myelin lamellae than in normal nerve, suggesting an atrophy of the axon. Biopsy of 19 sural nerves of patients with the neuronal type of PMA showed loss of large fibres (more than 7 micron in diameter). The number of small fibres was normal, presumably due to regeneration, since there were many "clusters" of small myelinated fibres. Fibres with demyelinated segments and onion-bulb formations were absent or rare and the endoneurial space was normal or slightly increased. Neither in the hypertrophic nor in the neuronal type did fibre loss occur selectively among the very largest fibres. Nine nerves from patients with hereditary spastic paraplegia and from a family with tremor and spasticity in addition to PMA showed changes similar in type but often milder in degree than nerves of the neuronal type of PMA. The number of unmyelinated fibres was normal in 12 of 21 nerves from patients with PMA; it was increased in 5 and diminished in 3 nerves.

Fibers in monkey posterior articular nerves

The distribution of axons in the posterior articular nerves in rhesus monkey has been studied in terms of ratio of myelinated to unmyelinated fibers, and size of myelinated fibers. Conduction velocity measurements were also made. The nerves contained 2,000 to 2,200 unmyelinated fibers of 0.2 to 1.2 mum diameter. They contained 399 to 478 myelinated fibers, varying in size from 1.4 to 12.3 mum. Thus 80 to 85% of fibers in these nerves were unmyelinated. The maximum conduction velocity of 70 to 80 meters per second corresponded to an initial small deflection, with most fibers conducting at slower rates. These results are compared to previous reports which severely underestimated the number of unmyelinated fibers because electron microscope counts were not utilized. It is suggested that pain fibers from the knee joint of monkey make up much of this large population of unmyelinated axons. An unknown number of post-ganglionic sympathetic fibers is also included in the unmyelinated fiber group.

Unmyelinated preganglionic fibers in frog ventral roots.

It has been suggested that the preganglionic visceral fibers in the frog are unmyelinated. To obtain further evidence for this suggestion: (1) the percentages of unmyelinated fibers and the myelinated fiber histograms were done for all frog ventral roots, (2) the number of unmyelinated fibers were counted on either side of a chronic section of the seventh ventral root and (3) compound action potentials were obtained for roots 7-10. The results are that slightly more than 80% of the unmyelinated fibers in the seventh ventral root arise in the spinal cord and are presumably unmyelinated preganglionic efferents. Furthermore, a C fiber volley could be followed from the seventh ventral root into caudal parts of the sympathetic chain. Thus this data provides confirmation for the idea that many frog preganglionic fibers are unmyelinated. This study also shows that 24% of the ventral root axons in the frog are unmyelinated and that, on the basis of percentages of unmyelinated fibers and myelinated fiber histograms, there are five categories of frog ventral roots.

Neural intersegmental connection in the spinal root and ganglion region of the rat.

A study has been made of the macroscopic, microscopic and electron-microscopical appearance of intersegmental neural connections in the rat. Macroscopically, spinal roots and ganglia of adjacent segments were frequently observed to be linked by discrete, slender strands, mainly in the lumbosacral region where the roots are long. When examined under the light microscope, even the smallest was found to contain as many as 72 myelinated fibres with a range of diameters between 1.5-14 mu-m. The were commonly accompanied by blood vessels. Connections, when present, contributed to as much as 6-28% of the total number of myelinated axons in dorsal roots. Under the electron microscope, links between dorsal roots, or between dorsal roots and adjacent ganglia, contained unmyelinated fibres comparable in numbers to those found in the dorsal roots themselves. In links between ventral roots and ganglia the numbers of unmyelinated fibres proportionally exceeded those found in ventral roots. The presence of these connections may account for the reported finding of undamaged nerve fibres in the dorsal roots after dorsal root sectioning or ganglionectomy and in the ventral roots after ventral root sectioning.

UNMYELINATED FIBRES AND SCHWANN CELLS OF SURAL NERVE IN NEUROPATHY

Electron micrographs of 45 sural nerves from patients with acquired (22) or heredodegenerative neuropathy (23) were analysed with respect to the number of unmyelinated nerve fibres, 37 nerves with respect to the number of Schwann cell sub-units and of structures connected with Schwann cells. Findings were compared with those in 6 nerves from control subjects and referred to the total number rather than to the number per mm2 to eliminate error due to increase in the transverse endoneurial area, present in more than half the diseased nerves. Ninety-one per cent of the diseased nerves showed one or several abnormalities in unmyelinated fibres of their Schwann cells. The best indicator of fibre loss was an increase in the number of Schwann cell sub-units devoid of axons, found in more than half the nerves. This was the only abnormality related with decrease in number of myelinated fibres. The increase in number of empty Schwann cell sub-units was due both to loss of unmyelinated nerve fibres and to proliferation of Schwann cells. Proliferation was indicated by the higher incidence of Schwann cell nuclei in cross-sections of diseased nerves than in controls. The earliest sign of involvement was an increase in number of profiles and of small isolated Schwann cell projections, observed in 33 of 37 diseased nerves, as the only abnormality in 7 nerves. The number of unmyelinated nerve fibres by itself was of little value to indicate loss of fibres, since regeneration often replaced or more than replaced degenerated fibres. Regeneration was indicated by an increase in number or incidence of small unmyelinated fibres, present in nearly half of 45 diseased nerves; and by an increased in the total number, present in a third of the nerves. An increase in the number of collagen pockets and of fibres undergoing degeneration (loss of organelles) and a decrease in the number of unmyelinated fibres per Schwann cell sub-units was present in only a quarter to a third of diseased nerves and was not related to other criteria of loss of fibres or of regneration.

Quantitative studies on the intermediate nerve of the mouse with the electron microscope.

Quantitative counts of the intermediate nerve fibers of the mouse with electron microscope have shown that, on an average, 1,267 (79.3%) and 301 (18.9%) of the total nerve fibers (1,597) were myelinated and unmyelinated fibers, respectively. The number of unmyelinated fibers in the intermediate nerve was less than one-half the number of unmyelinated fibers in the greater petrosal nerve found in previous studies. Therefore, it is postulated that some of the unmyelinated fibers in the greater petrosal nerve may come from the intermediate nerve, while the rest may be derived from another source.

Conduction in unmyelinated fibres in experimental neuropathy.

Conduction velocity of autonomic unmyelinated fibres has been measured in the cervical sympathetic trunk of normal rats, and in rats intoxicated by acrylamide or by isoniazid. The mean maximal conduction velocity in nerves from normal rats is 2·0 m/sec. There is no significant reduction in velocity of the unmyelinated fibres in nerves from intoxicated rats, although histological studies of the sural nerve confirmed severe degeneration of myelinated fibres in the same animals. It is shown that the amplitude of the compound nerve action potential is proportional to the resistance between the recording electrodes. If this is taken into account, there is no reduction in the amplitude of the monophasic action potential of unmyelinated fibres recorded from the cervical sympathetic trunk of intoxicated rats. The amplitude of the A component of the sural nerve compound action potential is markedly reduced in rats intoxicated by acrylamide or by isoniazid, but there is no significant reduction in the amplitude of the C component in the same nerve. It is concluded that in the rat an insignificant number of unmyelinated fibres of autonomic or dorsal root origin are affected in the neuropathy produced by acrylamide or isoniazid. The relevance of these findings to human neuropathies is discussed.

A quantitative electron microscope analysis of peripheral nerve in the urodele amphibian in relation to limb regenerative capacity.

AbstractAn approximate 1:1 ratio of myelinated to unmyelinated fibers was established in counts from electron micrograph montages in nerves of the newt, Triturus (Notophthalmus) viridescens. The number of myelinated fibers correspond to the number counted with the light microscope after osmium fixation. Light microscope counts of silver impregnated sections yielded a value slightly higher suggesting that, except for bundles of unmyelinated fibers, the silver technique revealed mainly myelinated fibers. The results were used to reassess previous quantitative studies on the relation between number of nerve fibers and the control which nerves exert on regeneration. For a truer estimate of the number of axons affecting regeneration, fiber values previously reported should now be doubled to include the large number of unmyelinated fibers. However, calculations show that the unmyelinated fibers contribute less than 3% of the total neuroplasm in the peripheral nerve.Finally, counts made of Schwann cells and fibroblasts show that the latter are few in number.

The sensory innervation of the pineal organ in the lizard, Lacerta viridis, with remarks on its position in the trend of pineal phylogenetic structural and functional evolution.

The sensory innervation of the pineal organ of adult Lacerta viridis has been investigated. Some specimens of Lacerta muralis lillfordi were also used. In the pineal epithelium, a small number of nerve cell pericarya of a sensory type are present. They lie either solitary or in small clusters close to the basement membrane. The axons originating from the nerve cell bodies, i. e. the pineal sensory nerve fibers, first course in the intraepithelial nerve fiber layer which is only locally present and contains a restricted number of unmyelinated fibers. In Lacerta viridis, the pineal fibers generally leave the epithelium at the proximal part of the organ proper. They then form small bundles which run along the outer surface of the basement membrane in the leptomeningeal connective tissue covering. At the proximal end of the pineal stalk the single bundles assemble constituting the pineal nerve. In Lacerta muralis the fibers leave the pineal epithelium at the proximal end of the stalk running farther down within the epithelium. Many fibers become myelinated after leaving the pineal epithelium. The pineal nerve runs ventralward in the midplane just caudal to the habenular commissure to which no fibers are given off. Continuing their ventralward course between the habenular commissure and the rostral end of the posterior commissure which is traversed by some of them, the pineal fibers reach the dorsal border of the subcommissural organ. Small separate aberrant pineal bundles traverse the posterior commissure at various more caudal levels. Having reached the dorsal border of the subcommissural organ, part of the pineal fibers continue their ventralward course directly running along the lateral sides of this organ to reach the periventricular nerve fiber layer lateral and ventral to it. A restricted number of fibers first turns in a caudal direction running between the base of the posterior commissure and the base of the subcommissural organ before turning ventralward to reach the periventricular layer. Most probably, pineal fibers do neither join the posterior commissural system nor innervate the subcommissural organ. Once having reached the periventricular layer, some pineal fibers curve in a rostral direction while others, before doing so, send a collateral in a caudal direction. Both, the main fibers and the collaterals, contribute to the formation of the periventricular layer. The sites of termination of the pineal fibers could not be ascertained.

Myelinization of the Optic Nerve and its Dependence on Visual Function— A Quantitative Investigation in Mice

ABSTRACT Quantitative studies have been made of the number, myelinization and diameter of the fibres of the optic nerve during post-natal development in black mice, using phase-contrast and electron microscopy. The influence of complete darkness was investigated. In mice reared in the light no myelinated fibres are present up to 5 days of age, whereas a few hundred are demonstrable at 10 days. Between 15 and 20 days of age, myelinization is intense, the mean number of such fibres per nerve being about 22,000 at 20 days. After this time there is only a slight increase, i.e., to about 25,000 at 30 days. Up to 30 days, only a few per cent of the fibres are more than 1 μ. in diameter (measured in fixed and embedded specimens). In adult mice, three maxima in fibre diameter are observed; the largest group comprises those with a diameter less than 1 μ. (0·6–0·8 μ.), and the two smaller ones fibres more than 1 μ. in diameter (1·1–1·3 and about 2·0 μ.). The fibres are found to be more closely packed in the central part of the optic nerve than in its peripheral parts, but the coarser fibres are more numerous peripherally. No appreciable number of unmyelinated fibres is visible in mature animals. In mice reared in complete darkness for 20 and 30 days, delay in myelinization of the optic nerve fibres causes a reduction in the number of those myelinized by some 12–13 per cent. The coarser fibres are affected to a greater extent than the thin ones; thus at 30 days the number of those more than 1 p in diameter is reduced by almost 60 per cent. In mice reared in darkness, a retardation is observed in growth of the nuclei of the retinal ganglion cells, as well as in their shape maturation (decrease in eccentricity).

The application of x-ray diffraction and electron microscopy to the study of human peripheral nerve obtained by biopsy.

Human peripheral nerves obtained by biopsy from patients suffering from neuromuscular disorders have been studied by x-ray diffraction and electron microscopy. Few abnormal diffraction patterns have yet been recorded and their significance is not yet established. Electron micrographs have revealed wide variations in the numbers of myelinated fibres included in the nerve trunks and have facilitated a detailed study of the Schwann cell-axon relationships in the large numbers of unmyelinated fibres always present. Some indications of demyelination have been encountered.